<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <div style="height: 2000px;background-color: red"></div>
    <div style="position: fixed;height: 20px;bottom:0;right:0">返回顶部</div>
</body>
</html>